I have the Ryobi 40V lawnmower, chainsaw, and pole saw. (they're great!)

For really hard woods I get about 30-45 min out of the chain saw per battery. I use it for chopping up fallen trees (I live in a heavily-wooded area) so haven't done firewood exactly. I have 2 batteries and I get tired before I run down the second one.

Its kinda fun how it goes from dead silent to ripping through a tree. Although the bar length is probably too short for your needs. Plus a cord is a lot of wood (to me).

I figured anything that needs a more powerful chainsaw is best left to a professional anyway, so the battery-powered saw acts like a built-in buffer on hurting myself.